This invention relates generally to providing security for the Publicly Switched Telephone Network (PSTN) and more particularly to using packet-switched communications to authenticate identity assertions made over the PSTN.
Caller Identification (Caller ID) and Automatic Number Identification (ANI) are two mechanisms to indicate the identity of a PSTN caller. In general Caller ID is not policed or controlled by any service providers, and as a result, callers can easily make false Caller ID identity assertions without being caught. For example, a caller with access to an Integrated Services Digital Network (ISDN) could set the Caller ID field on the D channel to any value to make a false identity assertion. The caller could then use a Terminal Adapter (TA) to transfer an ISDN communication with the false identity assertion to the PSTN. Since service providers in general do not police the Caller ID field, the caller is unlikely to get caught.
ANI is only slightly more secure than Caller ID. Even though ANI does include an ANI II field indicating whether the network or a subscriber inserted an identity, not all service providers police the ANI II field. Moreover, service providers in some countries allow users who have changed the ANI value to access the ANI II field and falsely indicate that the network inserted the identity.
The ease at which users can make false identity assertions over the PSTN using Caller ID or ANI values is problematic. For example, criminals can insert a false ANI value when calling a financial institution to get past initial security checks by appearing to be calling from a customer's home. Similarly, criminals, collection agencies, and private investigators could change the Caller ID value to impersonate another for generally malicious reasons. Neither the ANI nor the Caller ID are cryptographically secured, and rely completely on trusting the previous service provider or previous network element.
Because of the forgoing limitations, identity assertions over the PSTN are unreliable. The disclosure that follows solves this and other problems.